The chemistry of line marking - anyone for tennis?

What kinds of paints are used and what are the components?

Typically, all line marking paints are water-based formulations. These are composed of a resin (usually a vinyl acetate copolymer or a styrene-acrylate copolymer), white pigment (titanium dioxide), pigment dispersant, thickener, defoamer, and sometimes other additives to control properties related to storage and application.

This sounds easy. Can I just go and buy some white paint from a DIY retailer?

Well, no. The machines used in conjunction with line marking paints either use a transfer wheel or spray application mechanism to apply the paint to the grass.  Therefore the opacity of the paint and its rheology must be optimised for either process. If you took typical wall paint and put it inside one of these applicators, it would likely be too thick to apply and if you add even just a little bit of water, the viscosity will significantly reduce to the extent it would be like trying to paint water. In addition, the opacity of the coating would be very poor too, requiring a significant number of recoats.

Figure 1: The method of dispersion is important to consider when formulating a coating.

So what makes line marking paints so special?

Typically, line marking paints for grass are supplied as concentrates so the grounds person has to dilute it, as specified by the manufacturer, for the painting appliance being used. 

Line marking paints are usually characterised by a high titanium dioxide content so that after dilution, the paint has sufficient opacity so no recoat is required.  However, this can make the formulation expensive. Therefore, it is possible to replace some of the titanium dioxide with a suitable high opacity, mineral filler to reduce costs. A suitable material would be calcined kaolin such as Satintone 5HB. By replacing between 10-20% of the titanium dioxide (by volume), it is possible to retain critical properties such as opacity and brightness.

The high pigment concentrations present in line marking paints also present challenges in the dispersion and prevention of syneresis (sedimentation). 

For most line marking paints, a suitable dispersant such as Edaplan 516 can be used with low addition rates to lower the mill base viscosity making the high pigmentation levels possible. In addition, Edaplan 516 prevents agglomeration of the pigment particles during storage and flocculation upon dilution.   

As titanium dioxide pigment has a high density, it is always at risk of causing sedimentation over time during storage.  A very effective way of preventing this is with a suitable additive such as Attagel 50.  This is a rheologically active mineral that can create sufficient structure within the paint to prevent the settlement of the pigment. Low addition levels of about 0.5-1.0 % are usually very effective.

What about other outdoor sports surfaces including artificial grass?

These present additional considerations such as coloured pigmentation, durability and adhesion for example which will be discussed in a subsequent article.

Figure 2: Different additives can provide the paint with the different qualities it needs to be easily applied to the grass courts.

If you have any questions or want to discuss a coating formulation, please give us a call and one of our technical team will be able to advise you.